The older I've gotten, the more I'm convinced that people don't care what the clock on the wall says, what they care about is minimizing the effects of sunrise/sunset. No one wants to be awake or get their kids awake before sunrise, and many jobs can't continue after sunset. Lifestyles will adjust forwards or backwards to match the hours in between
Yes, we are diurnal animals. Yes, sunlight matters to how we sleep. But why do we care whether the hands on the clock are pointing up when the sun is highest overhead? Everybody could do what they needed to do sleep wise regardless of where they were pointing.
The simplest solution is not only to do away with DST, but to adopt a single universal time. This would make keeping in synch easy. No longer would time zone conversions be necessary. No longer would we have to adjust our sleep schedules twice a year or worry about whether whomever we had to collaborate with in a different part of the world was doing the same.
But outside a handful of industries and technical fields, we seem unable to stomach the thought that the clock might read 17:00 as the sun rises. and 7:00 as it sets. That's just too weird. And why should Tavarua have to tolerate that when Greenwich gets to live with the historical norms?
Politics. Politics are the end reason for why we fight over what the clock says.